Radio communication checking system



B. c. I oRD 2,433,281

RADIO CQMMUNICATION GHECKING SYSTEM Original Filed April 12, 1941 v 8 Sheets-Sheet 1 Deb. 23, 1947.

DCC. 23, 1947. B, C, LCRD 2,433,281

RADIO COMMUNICATION CHECKING SYSTEM Y Original Filed April l2, 1941 8 Sheets-Sheet 2 vTIVO CHA NIVEL F /L TER T HANS SWITCH A rm /vs/-ER R5 .AY

maman/fren Y l Rscf/ van Y pome-R l ANT TRANSFER 4 RELAY 'fA/.fAM//v CLG/50 Y INVENTOR ATTORNEY Dec. 23, i l BEC. LORD .2,433,281

RADIO COMMUNICATION CHECKING SYSTEM Original Filed April 12, 194:1V 8 Sheets-Sheet 3 RICE/VER ANT. COMA/6770 70 F/LAME N T5 5M/A M//V C Oka 1 N VENTOR.

ATTORNEY.

Dec. v23, 1947. M B, c, LORD A, 2,433,281

RADIO COMMUNICATION CHECKING SYSTEM origina; Fiied April 12, 194i 8 sheets-sheet 4 F/GURE 3 EM/AM//v C. awa

A INVENTOR.

BYl

. XTTORNEY.

De@ 23. 1947. a. c. LQRD l 2,433,281

` I RADIO COMMUNICATION CHEC-KING SYSTEM -Original Filed April l2,. 1941 8 Sheets-Sheet 5 NToR ATTORNEY RADIO COMMUNCATION GHECKING SYSTEM Original Filed April 12, 1&941 8 Sheets-Sheet 35M/Anw C Oka INVENTOR ATTORNEY Dec. 23, 194,7. B. c. LORD 2,433,231

' RADIO COMMUNICATION CHECKING SYSTEM y 0rgina1 Filed April 12, 1941 8 Sheets-Shea?I '7 RADIO COMMUNICATIQN GHECKING SYSTEM originl Filed A pril 12, 1941 8 sheets-sheet s EM/AM//v C? cv/P0 INVENTOR ATTORNEY Patented Dec. 23, 1947 cation for U. S. Letters Patent Serial No. 388,338, filed April 12, 1941.

The system of the Halstead patent involves the use of electric wave energy for communicating naling zones by means of speech signals and audio-frequency control signals which serve to selectively actuate visual to specic tralc signaling elds, an example of which may be that of railway classication yard improvements havebeen found to be desirable system to the conditions peculiar to the par- For example, it has been determined that two-way radiotelephone communications between a central point -or primary station, and operators of locomotives, or secondary stafio and Safe Operation f Vehlcles Within the signaltions, within a terminal area, or main line track section or zone is desirable, and that constant periodic test pulse transmission from the central or primary station of a protective aural and visual ticular service.

particular 4value in preventing damage to equipment or operating personnel in the event of failther detailure of the control station transmitter or vehicle receiving equipment. Also, it has been found responsive to wave energy transmitted from a remote transmitter, which may be on a vehicle or secondary station, whereby the periodic pulse mary transmitter are suspended while signals This invention pertains to traiiic signaling, and 1n particular relates to a traic control and comsecondary transmitter. munications system of the general type as disclosed in the Halstead patent, Reissue No. 21,818,

RADIO COMMUNICATION CHECKING SYSTEM Benjamin C. Lord, Valley Stream, N. Y., assignor, by mesne assignments, to Farnsworth Research Corporation, a corporation of Indiana Original application'April 12, 1941, Serial No. 388,338. Divided and this application August 14, 1944, Serial No. 549,390

18 Claims. (Cl. Z50-6) UNITED STATES "PATENT OFFICE are being received from the remote mobile or .Although the system of the present invention is particularly applicable to signaling in large granted June 3, 1941.` It is a division of appli- 5 terminal areas, such as classification yards and on railroad main line, the embodiment of the invention as described herein is illustrative only, and represents a specific example of the application, therefore, does not constitute a limitation intelhgence t0 traffic Within predetermined sig- 10 since the flexibility of the system is such thatit maybe used in other vehicle communications and signaling services, such as -in airways, airindicators, such as ports, and in various municipal fire and police stop," "gof 01 Caution Signal lightS- The radio circuits where two-way communications audio-frequency control signals may also S0 be 15 with mobile or secondary station units 'are used. rendered audible, to serve as an aural check, or

test pulse, by means of the same electro-acoustic apparatus that is employed for reproduction of the speech signals.

The present application incorporates certain of 2o the principles disclosed in the original system and include improvements and modifications for effecting two-Way radiotelephone communication as well as protective visual and aural signaling, for the purpose of attaining positive, centralized control of trafiic or other signaling operations within a given zone or Zones in which a two-way communications service to vehicles is involved.

The present embodiment of the invention embraces a coordinated aural-visual communications and signaling system constantly under supervisory control of automatic protective, or checking signal circuits. modulated by voice and control signals is transmitted from a control station to vehicles within a given signaling zonein which operations are conducted under the influence of the control station. Receiving equipment on all vehicles within the zone, may, if desired, be tuned to respond to carrier wave energy, of a predetermined zone frequency, which is transmitted from the control station. Thus, the operator of the control sta- In applying the System of the Halstead patent tion may be the central coordinator of all movements of vehicles, such as locomotives, within the or main line signaling, certain modifications and Sgnaflmg Zone' 11h15. Zone m the case of Classl" cation yard signaling, may extend from the in order 1-,0 .more effectively adapt the Original 35 transmitter in every direction throughout a yard area, or it may be localized along speciic lanes of tralc by directional wave-energy transmitting systems as disclosed in the Halstead patent.

In order to more completely ensure efficient Carrier wave energy,

ing area, automatically transmitted periodic checking signal indications are provided in both the control station and in vehicles. permits continuous supervision of operation of checking signal at predetermined intervals is vof i5 control transmitter equipment and receiving units in all vehicles as will be described in fur- It is desirable in any traic signaling and communication system in which orders of any nature desirable to provide an automatic control means, so are DeriOdiCally transmitted to moving Vehicles for their direction to provide a means for the prevention of accidents which might result from failure of the transmission and reception .equiptransmissions from the control station or priment. Suppose, for example, that a control dispatcher has given aural proceed instructions This to the engineer of a pusher locomotive located at the rear of a long freight train proceeding toward the hump of a classication yard. Under these conditions, particularly if Wayside signals arecbseured by a fog-onstorm, the-enl gineer Willgcontinue to move the locomotive untily another signal is received to caution him or to direct him to cease the movement. Should the control transmitter or locomotive receiving apparatus fail, the engineer would assume that heshould continue to move even though, in theV meantime, the control operator. has issued in.-

structions to stop. It is obvious that. the dis. patchers instructions would be inelectiye in.

bringing the locomotive to a stop, notbeing aware of failure of equipment. Under-this condition a serious accident might result.

Thus, in order that the engineer may ascertain at all times that the central station transmitter and locomotive receiver are in proper working order, any overalll protective checking system of automatic type is incorporated in the novell control means of4 the presentinvention. This checking systemL operates, in. a.4 general sense, uponv the safe-fail or circuit,v principle in. that. failure of any part` of the signaling system Will automatically be indicated'.

The. checking or. test pulsing system. comprises av continuously operative means for transmitting from. a control station. a periodic. test pulse or control signal of a. particular or distinctive form Whichmay be receivedby the engineer to indicate that. he is receiving signals from the control station.

In the illustrative. embodiment of theginvention describedV herein, the control or primary station emits. aY carrier. frequency, modulatedr by a particular audio-frequency which istransmitted periodically to the engineer. This signalis prefer ably in the f orm of a periodic series of impulses' which may. be manifest in the engineers cab by aural or visual means, or both.

This periodic carrier signal modulated by voice signals or by a particular control frequency may be. employed at the mobile or secondary station, receiver to energize a sound reproducer orto se lectively energize a particular checking or proceed indicator lampY in order that the engineer may know that he is incontact with the controlI station and may proceed in safety with a given order; Duringy the transmission of speech from the central or primary station, itY isV desirable. that the checking system ceases to. operate in order that an uninterrupted intelligible voice signal from the mobile unit or secondary.- station may be received. To effectA this function, vthe presentin-5 vention employs. a selective control circuit which automatically dispenses with the checking or proceed signals when the` central stationtransmitter press-to-talk switch is closed.'v

When the engineer desires to acknowledge the receipt of ag. particularv control signal, he mamby means of his transmitter send back @signal tothe control station. This may be .accomplished by voice signaling from the mobileunit, or by the simple closure of the transmitting switch in .accordance with a predetermined code, which, when received at the controlstation, .will automatically' cause the visual operation of a carrieractu-ated signal light.

In order to prevent'interference'with the ref ception of a voice sig-nal from a locomotive transmitter or secondary station, by the periodic actuation of the central transmitter, a novel, carrieractuated "lock-out circuit is employed tov auto.-

matically preclude operation of the central station transmitting operation and to keep the central station receiver in its normally on condition While a carrier signal is being received. This lockout circuit also' serves to prevent manual operation .of the. central` trausmittqert as. longas a carrier Wave from a locomotive or secondary station isV being received. A visual indication of reception of a carrier Wave from a locomotive transmitter is also providedfor supervisory or acknowledgment purposes. Thus, by means of automatic controls andvvisual signal indicators, a coordinated: signaling system of highly dependable nature isV provided. The possibility of simultaneous operation of both central station and mobile transmitter isalso obviated. Thus:

It is an object of this invention to provide a novel traffic signaling system for transmitting speech. and protective control or checking signals to traic within a signaling zone.

It is an additional object ot this invention4 to provider a novel two-way` traffic communicating; system forl transmission and reception of visual and aural, control or checking signals. within a signaling zone.

It is a further object. of this invention tollrovide means whereby a control signal, from a primary carrier Wave transmitter will lock-out and prevent operation ofa remote secondary transmitter while said primary transmitter is emitting a carrier wave signal.

It is another object of this invention to provide. means whereby a periodic signal is automatically emitted at predetermined intervals from a signal transmitter at one station to a cooperating receiver at a second remote station to serve as a checking, or supervisory, signal for. indicating that said transmitter andl said receiver are operative.

Another object of this invention is to provide a traie communications and control system for coordinating the movements of vehicles in a traffic area which is effective to automatically indicate failures in the transmissionA andl reception` system, operation being made onY the safe-f4ail' principle.

Another object of the invention is to provide for a comprehensive centralized traflic control System for a railroad freight classification yard; similar terminal area, or main line, wherein each of the locomotives or other vehicles is adapted to, re-Y ceive and transmit control signals, each relating to a particular traic operation, .and to provide. a comprehensive check onl the operating condition of the central station transmitter and locomotive receivers. Y

While these objects have been set out specifically herein, it is to` be understood that they are illustrative, and that other. objects may be,A or may become. apparent to a person skilled in the art from a perusal Qi thepresent dis-91.05.11@ Without departing from thesDrit-helieQf-- Referring t0. the drawings Figure 1. is a block. diagram. ofthe transmitting and. receivingcquirment employed at a central control station4 disposed. adjacent a. traflic signaling-Zone.

Figure 2 is a. block diagram .of transmitting and receiving equipment employed'in a locomotive or other vehicle operating Within the signaling zone ofthe central control station.

Figure 3 is a circuit diagram of transmitting equipmentemployed at the central control vstation..

Figure 4 is a circuit diagram of a present employed receiver utilized at the central control station.

Figure 5 is a front elevational view of one preferred arrangement of a. microphone, signal lights, .and a loudspeaker disposed at the central control station.

Figure 6 is a side elevational view of the apparatus shown in Figure 5.

Figure 7 is a circuit diagram of a present employed transmitter and receiver installed on a locornotive within the signaling zone of the central lcontrol station.

Figure 8 is a circuit diagram of a two-channel audio-frequency filter and checking-signal control relay and loudspeaker circuit employed in the present embodiment of the invention.

Figure 9 is a front elevational View of a present preferred arrangement of a microphone, signal 1 lights, and exible support are employed in the locomotive.

Figure 10 is a front elevational view of the microphone and signal light unit of Figure 9 with the front cover removed. 1

Figure 11 is a side elevational View of the microphone and signal light arrangement, showing the disposition of a shock-mounted microphone and signal lights Within a housing such as illustrated in Figure 9.

Figure l2 illustrates a present preferred disposition of voice and protective signaling equipment of the system within a locomotive cab.

Referring now more particularly to Figure 1, there is shown a schematic representation of the central control station transmitter and receiver. This iigure is merely a diagrammatic representation of the more detailed circuit diagrams shown in Figures 3 and 4 and the following description of the component parts will correspond for all of these figures.

The central control station may be located in the most accessible point of the limited area over which coordinating signals are to be transmitted. Thus, if the system to be described is applied to a freight classication yard, the central station may be disposed most conveniently adjacent the hump. The transmitter and receiver at the hump may be remotely controlled from one or more points if desired.

From these control points, the hump conductor, yard master or other control station operator may be in a position to best determine the nature of the signal to be transmitted to locomotives equipped with coacting signaling apparatus, which may be of the form diagrammatically illustrated in Figure 2,

Essentially, the central station includes a com: bined transmitter and receiver for establishing two-way voice communications and automatic As is illustrated in the embodiment of the invention shown in Figure 1, a receiver 2| and a transmitter 22 utilize a single antenna 23 which is joined to the transmitter or receiver through an antenna transfer relay 24. The receiver 2l may comprise conventional equipment for demodulating and amplifying a modulated signal radiated from the antenna 5| which is energized by a transmitter 52 (Figure 2) disposed upon a locomotive or a similar vehicle. The signal radiatedfrom antenna 5|' is intercepted by antenna 23 at the central station and applied to the receiver 2| (Figure l) which in lturn applies the 6 demodulated signal energy to a loudspeaker 25 'for rendering the received signals audible.

The transmitter '22 at the control station may also comprise conventional equipment for amplifying electrical signals impressed upon the input circuits thereof and causing these signals to modulate a radio frequency carrier which is then radiated into space through antenna 23 for reception by antenna 5| of Figure 2 and its coacting receiver 53 disposed upon a movable vehicle.

The signals applied to the input of transmitter 22 may comprise voice currents generated in microphone 26 or a constant amplitude audio frequency control signal generated at source 21 for utilization by protective checking apparatus at the central station illustrated in Figure 1 and corresponding apparatus at the movable station indicated in Figure 2 for constantly providing periodic indication of the proper operation of all these circuits.

This audio-frequency control signal is coupled to the transmitter through a transfer relay 3| which is manually controllable by a suitable switch such as the foot switch 32. Under normal conditions, the transfer relay 3| is in a position Where the audio frequency energy from signal source 21 may be applied to the input of the transmitter 22. The antenna transfer relay 24 is normally in a position for applying the signals intercepted by antenna 23 to the receiver '2 The receiver 2| and transmitter 22 are en-Y ergized from any available power source which may comprise batteries or alternating current. The laments of the various vacuum tubes utilized in these circuits are continuously energized Whereas the plate circuits of the transmitter and receiver are selectively energized from a high voltage source connected with either the transmitter or the receiver through the power transfer relay 33.

The movable members of the power transfer relay operate simultaneously with the movable members of the antenna transfer relay 24. Thus, when the antenna 23 is coupled to the receiver 2 I, the power transfer relay applies the high voltage to the plates of the receiving tubes. Conversely, when the antenna transfer relay interconnects the antenna 23 and the transmitter 22, the power transfer relay serves to permit the energization of the transmitter vacuum tubes and to deenergize the plate circuits of the receiver 2|.

An automatic keying device 3d is continuously operated and under normal operating conditions determines the movement of the power transfer relay 33 and the antenna transfer relay 34, and effects periodic operation of the relays.

The keying device 34 is employed to apply an energizing voltage to power transfer relay 23 and to antenna transfer relay 24 at regular intervals.

When this energizing voltage is applied to the relays, a signal is radiated which is a radio frequency carrier modulated by the constant-amplitude audio-frequency control signal provided by the control signal source '21. This energizing voltage is of a relatively short duration and thus the radiated checking signal is in the form of a plurality of periodic modulated impulses.

` During the normal non-keying portion of the operating cycle of the keying device 34, the power 'transfer relay 33 and the antenna transfer relay 24, are in the normal position, which, as previously mentioned, permits receiver 2| to remain in a normally-on condition to accept incoming signals from a transmitter of the type indicated in amsaem e-E'igufev 2,-.:a-nd to .impressethem-.upon loudspeaker v.Accorxlinglmthe centraly station., duringits op- .eration transmits a. series -otr -periodic` .impulses tandis, in-afposition .for receiving signals-in :the r...intervening time. '-If the operatoriofrthe central .control station.' desires to. transmit `instructions -to.the vehiole-carryingthe apparatus illustrated .in lfigure 2,.. operating.A within the-localized areas suchf-a-s the freight classification yard; the switch `..lated..signal .will beradiated from antenna-2&2.v

The central station .circuitswillbe in4 a condition for transmittingspeech signalsas longias. switch 321s closed.

' `When the desiredinstructions have been. given by the control operator, .the release of switch $8.

will then automatically disconnect. themicro- ,phone and applyfthev control signal.; generated within source 2 to the inputcircuits ofthe trans- `mittel: and the keying device-3d will again resume control of the sequential application. fof power yto 'the plate circuits of the receiver and transmitter and the corresponding application of the an- 'tenna 23.

The-central control station is provided with a `'plurality of pilot'lights which indicate proper operation of the entire two-way communication sys- 4tem -These pilot lightsare disposed in the operatorsfii'eld of vision to facilitate checking operations. A pilot light '35 is provided to indicate the' fact that a modulated carrieris'being radi .rated from antenna during Ythe-operationof the '.Ltransmitter. This vis-accomplished by'a'circuit which.is inductively coupled'tov the transmitter "..antenna circuit.

.-.Aswill be:hereinafterY explained, vthe signal inducedin'this circuit is applied-toa'demodulating and audio-frequency signalre'ctifyingy vcircuit 35 -.-which causes the .operation-of .arel'ay liwhen a modulated signal is beingradiated. The relay 3l in .turn energizesthe transmitting monitor signal'.f55

:.light'. `It isevident that during the normal operating cycley the monitor light' 35 willbe energizedperioclically'bt the.v modulated carrier which is. caused-to -be .-periodically* transmitted .by the keyei-.z 34.

.,.An additional `Visual.indication for the operator of. the .central station. is..a .transmitting indicator lighti whichrisenergizedwhenever the power transfer relay. energizes the. platecircultsof the transmitter E2. Accordingly, Yduring the normal-4` ioperation .of the. control station,l the-monitor indloatingflight 35 andlthe transmitting pilot light d l will be energized in unison.

On theother hand, when. the foot-switch "is operated for the transmission ofspeech, the *transmitting indicatingflight il willbe 1continuously'V energized to indicate ther application of 'power whereas .the monitor lightY 35 will ,.ashrin accordance with the impressed signal voltage during speech transmission ono'ther modulation.

When antenna ZSis-:energizech by signals-from a vehicleV operating withintthe classication-yard or other such area, the receiver 2| operates'fito :demodulate -these signalsiand-impress they demodulated energy u-ponloudspeaker 25.

Tok prevent interference with an incoming signal from a locomotive transmitter by the automatic .orfmanualoperation of .the central transmitter,

a novel carrier-operated transmitterl lock-out control circuit is provided-whichautomatically causes fthe periodic keying 'circuit' -35 f and linputtransfer relay 3l tolose control over 'the operation of the power transfer relay 23 andv 'thefantenna transfer relayi 25. This .lockout. condition will .exist asflongA as a carrier-wave from a-locomotive v transmitter -is 'beingv received' at the centralwstation. v

-.To eiect this control 'function a carriere'cony.trolled lockout relay 42 -is providedin' .the audio amplifying and -noise suppressioncircuit of the receiver 2l and operates whenever av carrierfis -received by antenna 23 from a transmitter 'such fas. 52` indicated in 'Figure'.2. :This relay-when energized automatically f disconnects: the keying .device liand .transfer relay 3i and thus permits the continuous reception ofenergy hy-receiver 2| .In order toV provide an indicationtthata carrier wave .is vJoeing received the lockout relay'talso serves to energize an indicating light-11.3 "which `again ispreferably disposed in theoperators-nor- Ymaliieldiof vision.

Itis evidentV that this -novely systemrprovides `means Vwherebysignals Yfrom -a-vehiole -may be receivedI aurally through the e agency -of Yloudspeaker: 25. or visuallyv by -pilot light- 431or1both. Thus, since theclockout relay isoperated by an incoming carrier wave'vtransmitted from' the vehicle .transmitter 52 illustrated-in Figure 2, the

"if it is .not convenient for him'to speak into vhis operator-of vthe vehiclemay;by'rnomentarily:keying his transmitter 52 through thefagency of a switch M, transmit anintermittent carrier^which will energize/pilotlight itin accordance.with any predetermined signaling Y 'codef Eof simple `form.

Thus,.fthe engineeremay acknowledge receipt'of an instruction, or conveyother lsignal intelligence microphone.

Therefore, it .may be seen that'ifthecentral station is arranged with the Variousfcircuitelements .diagrammatically illustrated-fin Figure 1,

'it will continuously and automatically transmita series of checkingorv controll impulses andV bein a position to receive signals in= the time-between impulses.

Furthermore, .the central stationoperator may transmit any desired speech signals. andmay receive incoming signals aurally and visually.

tion such as .thatindicatedin Figure 2. .If this cation yard, then the .radio1 apparatus of. Figure 2 may be.v most conveniently 'loca-ted 'withina the cab. of f.a locomotive orfupon they tenderihereof. y.65...lil-ssentially, .the mobile equipment?A comprisesA the tramsmitter` 52. and receiver-:53,1 each cooperable with rthefsirigle antenna 5| :through-"ai relayf55 .which selectively connects'thez antenna and the receiveror transmitter.

. Normally, .the transfer relayr isz-in a.position where antenna 5l is coupled to receiver. 53 so that signals radiated from antenna;23tatnthe'control -station willbeapplied to the 4receiving equipment at the locomotive. .-Thereceivedsignals afterloe- .ing demodulated- :in 'receiver circuits 53 are lap- 1l in the direct current supply. The alternating current impressed upon terminal 1| in addition serves to continuously drive a relatively small synchronous or other substantially constantspeed motor 8| which in turn drives a cam 82.

This cam, having a plurality of projections 83, operates to periodically close the switch 84 to permit the automatic keying of the transmitter as will be described in further detail. Essentially the transmitter comprises a radio frequency oscillator tube 85 having a tank circuit 31, the frequency of which is controlled by the crystal 86 in the grid circuit thereof.

The constant frequency output of the oscillator 85 is applied to the control grid of a power amplifier 92. The anode of this amplifier is energized from the high direct voltage source through a tank coil 93 and through a radio frequency choke coil 94.

The output of the power amplifier is in turn coupled to the antenna 23 through coupling condenser 95 and through antenna transfer relay 96. When the transmitter of Figure 3 is in the normal operating condition as illustrated, the closure of switch 84 under the influence of cam 82 will, as illustrated, energize the coil 91 of the antenna transfer relay 96 to couple the antenna 23 to the output circuit of the amplifier 92, and so permit the radiation of the signal generated at the transmitter.

Energization of the relay coils is secured through a small rectifying unit which is preferably of the dry-disc type energized through transformer |02 from the main alternating current supply.

As illustrated, an audio frequency control signal is impressed upon the input circuit of the transmitter. This signal, which functions as the checking signal described in connection with Figures 1 and 2, is preferably of a relatively low frequency alternating current and is thus most conveniently obtained by utilizing a harmonic of the alternating current power supply.

Thus, as shown in Figure 3, the audio frequency control signal is obtained from the input to the filter 11. A tap on variable resistor |03 is coupled through condenser |04 and through the switch members of the input transfer relay 3| to the primary of the input transformer |05. The secondary of the transmitter input transformer |05 is coupled to the grid of a tube |06, the anodes of which are energized from the high voltage source through the primary of a coupling transformer |01.

The terminals of the secondary of transformer |01 are coupled to the grids of a push-pull modulator tube The anodes of the tube ||l are joined to the terminals of the primary of a modulation transformer H2, the center tap of which is energized from the high voltage source.

In the modulating circuit, as indicated in Figure 3, the anode of the power amplifier 92 is coupled to the screen grid thereof through the tank coil 93 and the radio frequency choke 94. This parallel combination of screen grid and anode are then joined to the high voltage source through the secondary of transformer |2. Thus the signals impressed upon the input transformer |05 cause corresponding fluctuations in the plate and screen grid circuits of the power amplifier 92. The modulated carrier, as previously described, is coupled through condenser 95 to Ithe antenna 23.

As hereinabove set forth, when relay 3| is in the normal position, the transmitter input amplifier |06 is in a condition to be energized by the audio frequency energy tapped from power-supply resistor |03 and passed through condenser |04, and the switching members of transfer relay 3|. Thus, when power relay 33 is energized and power is applied to the transmitter, modulating signal energy is applied to the transmitter.

The audio frequency energy has a fundamental of twice the alternating current input frequency and thus may be of the order of cycles if a commercial power line is used for a power supply at the terminals 1 When the various relays are in their normal position as illustrated in Figure 3, it may be seen that the switching members of power transfer relay 33 preclude the flow of current in the primary of the plate transformer 13.

Accordingly, this precludes the energization of all the anode circuits of the transmitter since no voltage is impressed upon the anodes of the rectiler 12.

It is to be noted, however, that the transmitter is normally kept in a condition where the immediate energization thereof may be effected. Thus the primary of the filament transformer 14 is continuously energized from the power impressed upon terminals 1|. The plate transformer 13 is dependent upon the position of the switching members of the power transfer relay 33 for energization.

During the rotation of motor 8|, the cam projection 83 will close switch 84 and as may be seen from the circuit diagram, will thereby energize the coil of power transfer relay 33 from the voltage provided by the small full wave rectifier |0| provided, of course, that the coil of lockout relay 42 remains cle-energized and the switch contacts thereof remain in the position illustrated in Figure 3.

Energization of power transfer relay 33 will cause the switching members 33 to move downward as viewed in Figure 3 and accordingly will energize the primary 13 of the plate transformer. This will simultaneously cause the application of a high direct-current potential to the anode of the various vacuum tube circuits illustrated and supply the low frequency signal to the primary of input transformer |05.

The coil 91 of the antenna transfer relay 24 is in parallel with the operating coil of power transfer relay 33 and consequently when the switch 84 is closed by the cam 82, the antennaJ transfer relay will operate to cause the arm 24 to move downwardly as viewed in Figure 3 and connect the antenna 23 to the .tank coil 93 through coupling condenser 95.

Therefore, the carrier modulated by a constantamplitude audio frequency control signal is radiated into space when switch 84 is closed. Since the filaments of the various electron tubes are normally heated in this power transfer system, the transmitter will. operate instantaneously upon the closure of switch 84.

Continued rotation of the cam will open the contacts of switch 84 and rie-energize the relays 33 and 24 which will then resume their normal positions indicated in Figure 3 and the transmission of a wave will cease. Since, as previously described, the motor 8| operates at a substantially constant speed, the closure of switch contacts 84 will be periodic and thus a periodic signal comprising a radio frequencycarrier modulated cassatie by an Vaudio frequency signal will automatically betransmitted.

The rate at which these periodic signals are Si-nce, however, 'it is f desirable `in `this novel system to permit the-operator of the mobile station to `call' and Speak to the control station, these pulses are of relatively short-duration and mai7 normally be 'transmitted -at regular intervals of primarily the order of I'ifve-secondsapart.

-lSince'the-operation ofthe power transfer relaxT y313 ispe'riodic=inaccordance with the operationof switch contacts 84 the-'application of power to the transmitting circuits periodically occurs lfor a relatively -shorttime Therefore, since the modulatedcarrier of the-transmitter is only-generated ior Vrelatively short intervals, considerable economies are eiected rand the consumption of electrical `energy is greatly decreased.

-As hereinabove described, the monitor pilot light'35 shown irl-Figures l and 3 provides a visual indication of the fact that Va modulated carrieris being generated. VEnergy for-the operation of the relay controlling vthe pilot light'35is derived from inductive coupling withthe tank ycircuit of the transmitter. vAs illustrated in Figure 3, a coil I2 is inductivevly coupled Awith the tank coil 793.

The coil |2| is tuned@tothe-carrier-frequency bythe variable condenser-|22 and the potential appearing across this tuned 4circuit is impressed through theparallelV combination'of grid leak |23, and condenser |24 upon the control grid of an electrontube |25 which-functions in this instance as a grid-leak detector. `Theanode circuit of the tube |:25'is joined to the source ofhigh potential through rload resistor |126'a'n'd the output'of this tube is coupled thro-ugh condenser |27 lto 'the anodes of a signal rectifier|13 I The vrectii-le'd modulating :signal energy then flows through thecoil'of the monitor relayfSl-It'o causethe'operation ofr contacts 3l' thereof. The contacts 3l'l are joined insseries with the monitor light and this series c'ircuit'is connected to -a power'source:suitablejfor energizing the monitor lighter.

In the r embodiment illustrated `ltr-Figure 13,v the monitor light-isy of a Vrelativelylowvoltage type and is energized Afrom `the -iilament supply obtained from transformer secondarylll. A 'condenser |32 is connected across the monitorlight niordertogprevent radio frequency energy, which mayjbe `present `in the -relay leads due tofstrat7 coupling, from 4being fed back into the input circuit by interconnectingcables.

Since the Ycoil of Vrelay3'l'is lenergized `by the rectified demodulated energy coupled from the tank circuit, .the.imonitorxpilot'light will flash, whenever Va 1 modulated carrier 'is ygenerated and a signal transmitted. 3The=relay3l will normally tend to follow the variations of the modulations which may,` if desired, be smoothed as desired by a lter l circuit vto preclude lchattering thereof. A .condenser |33-iszplaced-across the winding of relay 1.31 vto icy-pass the alternating current component .of the rectified;audiozfrequency signal.v

The `transmitter pilot flight l4| is .energized througnthe switching :members of `the power transfer relay 33 from the filament supply ofethe I4. transmitter. whenever plate `power is applied to itheitransmit.- ter circuits .and thus during .the vnormal operation of the central .station will flash periodically in accordance with the closing of Switch 84,

`If the central station operator desires to transmit amessage to the operator of a .locomotive'in the classification yard, thefswitch 32 is closed. This switch may be :any conveniently disposed normally open :switch and in the modification illustrated, it is a .foot switchadjacent the transmitter.

rClosure of this switch -will apply-.energy from rectier 1||l| to thelcoil of input transfer relay 3|, and accordingly cause the switching members 8 l1"` thereof to, movedownwardly and, as indicated, to interrupt the control .signal circuit from the tap on power-supply resistor |03 to the input trans former m5, Vand to complete the circuit from a microphone v2b to this input circuit.

In addition, the switching members of this relay complete a circuit from the high -voltage point of rectifier kliti `to the parallel coils of relays 33 and hprovided relay42 is not energized. These relaycoils, when energized as previously described, will apply a hig-h potential to the plate circuits-of the Yvarious vacuum tubes at the transmitter and will vconnect the antenna83 to the tank circuit of the transmitter. Thus, thetransmitter `is in a condition whereby speech energy impressedupon microphone itv isamplied and caused to modulate the ,radio "frequency carrier-in power ampliner ,$52, the energy from which is then radiated intospace through antenna 23.

Furthermore, the operation of relay 3| in disconnecting the source of constant amplitude audio frequency checking signal'from the input circuit ofthe transmitter precludes interference between speech transmission and the checking impulses despite the continued operation of motor 8| and the continued closure of switch 8,4. Therefore, the yoperator `of the central control station may transmit a message by operatingthe switch 32 and speaking into microphone 25. Since the receiver at the mobile unitisA normally in aposition for the reception of energy, theoperator of the Vcentral station may immediately establish communications with the operator of aA mobileunit lwithin-the same signaling zone.

.The receiver of the central station permits the reception of signalsf-rom the classification yard locomotive whenever the engineer .thereof desires to call in, check instructions, or acknowledgean instruction. This receiver -is normally in a position whereby lenergy f transmitted from Ythe locomotive station may be received,

The central station receiver illustrated in Figure 4,1and-in block'diagram, Figure 1,jis related to the central transmitter illustrated Figure 3 in "that a common antenna'may be employed in both circuits and that power for the operation thereofris. sequentially applied in a predetermined periodic ysignaling cycle as determined by the operation of synchronous motor 8| and associated cam 82.

7The power transfer relay 33 illustrated in Figureis'common to the receiver and to the transvmitter and these `are interconnected between the terminals Ml. Furthermore, the common antenna'23 illustrated inFigure 3 is connected to the -receiver'through antenna transfer relay 2 4 and 'through a connection joined to terminals |42-9I`2 at the receiver and transmitter.

When the-power transfer relay 3,3 andtheantennatransfer-relay 24 are in a position indicated This light wil-l -ftherefore operateI in Figure 3, the receiving circuits are energized and the antenna 23 is joined to the input circuits and thus places the receiver in a condition for the reception of signals intercepted by the antenna. The receiver may be energized from an individual rectifying circuit energized from the same source of alternating current and impressed upon the receiver terminals |43.

The plate transformer |44 and the filament transformer |41 are continuously energized from the terminating current source |43. Conventional filter section |46 is joined to the filament of the rectifier |45 for eliminating the ripple of the rectified potential. A bleeder resistor |48 is shunted across the output of the filter section |46. The high potential lead for energizing the plate circuits of the various electron tubes is broken at |4| by means of normally closed contacts 33 on the power transfer relay 33 as indicated in Figure 3. The interconnection of Figures 3 and 4 is shown by the corresponding terminals |4| on both figures.

The filaments (not shown) of the electron tubes indicated in Figure 4 are all continuously energized from the power transformer secondary |41, and thus, as shown in Figure 4, power is applied to both anode and heater circuits of the receiver.

Incoming signals intercepted by the antenna 23 are impressed upon a radio frequency transformer |5| the secondary of which is tuned by a variable condenser |52. A radio frequency amplifier |53 of conventional form is utilized to raise the level of incoming signals and the output thereof is coupledthrough condenser |54 to a grid of converter tube |55.

A beat frequency oscillator tube |56 utilizing a crystal |51 for frequency control generates a continuous oscillation which is coupled from coil |6I to another grid of the converter tube |55. This radio receiving circuit may comprise the conventional superheterodyne circuit for receiving and demcdulating incoming signals. Thus, the output of the converter tube |55 is coupled through an intermediate frequency transformer |52 to the control grid of an amplifier |63.

The output of this last-mentioned amplifier |63 is then coupled through the intermediate frequency transformer |64 to a second amplifier tube |65. This tub-e has a diode section energized through condenser |61 and having a, load resistor |58 which furnishes a negative biased voltage for automatic volume control as is well known in the art. The output of the amplifier tube |65 is also coupled to intermediate frequency transformer |69 to one anode |18 of the double diode rectifier tube |66. The variable potentiometer il! acts as a diode load and is coupled through condenser |12 to the grid |13 of the dual triode |8|.

The diode load |1| is by-passed by condenser |14 which acts as a radio frequency filter. This diode load |1| is also shunted by other diode section of the tube |66, and condenser H5. This acts as a noise discriminating and limiting circuit. The arm of the potentiometer |1| is connected to grid |46 of the dual triode tube |8| through the filter resistor |11. When no carrier is present the grid |l'6 is at zero potential with respect to its associated cathode, and therefore the effective plate resistance is very low. By means of the voltage dividing network comprising resistors |86 and |93, the grid |13 through its gridleak |19 is maintained at a high negative voltage with respect to its associated cathode. This high negative bias effectively reduces the amplification of the tube to a minute value an causes a cessation in the flow of plate current. When a carrier is present and amplified by the respective radio frequency and intermediate radio frequency amplifiers and rectified by means of the diode |66, a negative voltage appears across potentiometer |1|. This voltage when applied from the adjustable arm of the aforementioned potentiometer to the filter resistor |11 through the grid |16 of the dual triode |8| causes the plate resistance thereof to increase considerably in value. This by means of the aforementioned voltage dividing network causes the grid |13 to assume its normal operating bias with respect to its associated cathode. Thus, audio-frequency noise suppression is effected, under control of an incoming radio frequency carrier.

Therefore, plate current will flow through |82 and through the relay 42' causing the switching members to operate. Since the winding of the relay 42 has a high impedance to audio-frequencies, this winding together with the compensating resistor |92 acts as the plate load for |82 and thus the audio-frequency signals are coupled by means of condenser |63 and volume control |84 to the input grid of the power amplifier tube |85.

The output of amplifier |85 is coupled through transformer |81 in the anode circuit thereof to the loudspeaker 25 and to a plug |9| whereat earphones may be connected if desired.

The anode |82 is energized from the high positive potential through a parallel combination of load resistor |92 and the coil of suppressor relay 42. An incoming carrier intercepted by the antenna 23 and amplified and demodulated in the various receiver circuits illustrated in Figure 4 will thus cause the energization of the coil of relay 42 to cause the movement of switch members 42'.

This novel manner of actuating a lockout relay 42 inserted in an audio-frequency noise suppression circuit in accordance with an incoming radio frequency carrier is illustrated in both Figures 3 and 4 and the various connections of the switching members are best illustrated in Figure 3. Thus it may be seen that the energization of the coil of relay 42 due to a received signal will cause the movement of the switch members to open the series circuit of switch 84 and contacts 8|' between the coils of relays 33 and 24.

Accordingly, the continued operation of the switch 84 under the influence of the cam 82 will have no effect upon these circuits. The operation of the switch members of suppressor-actuated relay 42 also completes a circuit from the filament winding 14 of the power transformer to the call light 43 and thus when a signal is received, the calling light will iiash. An incoming signal will operate lockout relay 42 as previously described to preclude the operation of power transfer relay 33 and Iantenna transfer` relay 24 from the positions indicated in Figure 3.

Therefore, the reception of a signal will preclude the transmission from the central station of the checking impulse or speech transmission which would normally tend to interfere with the signal received.

As the antenna 83 is alternately switched from the receiver circuit to the transmitter circuit, reception will only take place when in the position shown in Figure 3. This permits the operator of a classification yard locomotive, by a mere transmission of his carrier wave, to maintain the cerlitral station in condition for receiving the signa s.

plify the audio-signal. The other section of tube 226 acts as a suppressor circuit as described in connection with the similar circuit of Figure 4. The signal is then coupled through condenser 231 to a power amplifier 24| the output of which is coupled through transformer 242 to an earphone connection 243 and a parallel two-channel filter (illustrated in Figure 8) through the terminals 3 and 4 of the connector 244 illustrated in both Figures '1 and 8.

Referring now to Figure 8, the filter section comprises essentially a parallel arrangement of high pass and low pass iilter sections joined to the terminals 3 and 4 of the connector 244. Thus, a low pass filter which may in one form comprise series chokes 245 and shunt condenser 246 will effectively block the passage of high frequency signals while permitting the unimpeded passage of low frequency signals therethrough.

The high pass filter in parallel with the low pass filter section joined to terminals 3 and 4 of connector 244 comprises essentially a plurality of series condensers 241 and shunt inductance 25|. This filter section then will preclude the passage of relative low frequencies while permitting the unimpeded passage of the higher frequency signals. The design of the filter will determine the extent to 'which attenuation of signals of various frequencies may be effected. Hence, the high pass lter section may be designed to pass a relatively small amount of low frequency energy to permit limited aural reception of the checking signal, if desired.

Accordingly, demodulated energy applied to the terminals 3 and 4 from the Output of the power amplifier 24| will selectively pass through filter circuits depending upon the nature of the signal. If the received signal comprises the low frequency checking impulses periodically transing signal will be rectied therein and as illustrated, the output thereof is impressed upon the coil 253 of the checking signal relay 62 illustrated also in Figure 2.

ASince the current is of a fluctuating nature, although rectified, a condenser 254 is shunted across the relay coil to preclude chattering and improper operation of the relay coil 258. Thus, it may be noted that the checking signal transmitted from the central station periodically due to the operation of synchronous motor 8| and correspondingly switch 84 will be received at the locomotive in the classification yard and will be demodulated and amplified and impressed upon a relay 62.

`The switching member 62 of this relay will therefore operate in a manner which corresponds with the operation of switch 84 during normal operation of the two-way signaling system. The closure of relay 62 as indicated in Figure 8 will short-circuit a section of a variable resistor 26|. This resistor 26| is joined in series through terminals and 2 of connector 244 indicated in Figures 7 and 8, with a checking pilot light 63 and the entire series circuit is connected between the direct current supply of the locomotive and ground.

Upon receipt of a checking signal, the contacts of checking relay 62 are closed. and a section of the resistor 26| is shortcircuited as determined by the position of the variable tap 263. Therefore, the checking light will flash to full brightness upon the receipt of a checking impulse and indicate in the manner described, the proper operation of the transmitting and receiving circuits. The output of the high pass filter comprising the condensers 241 and the choke 25| `is coupled through transformer 264 to the loudspeaker 51.

A received speech transmission will pass through the high pass iiltersection and energize the loudspeaker and so permit the central station operator to instruct the operator of the classification engine. The speech transmission will not effectively ow through the low pass filter and thus will not Venergize thechecking lamp.

The checking signals may, as described above, be permitted to energize the'loudspeaker 51 to provide an audible check on the operation' of the traffic communication system. Thus, the checking signals will periodically cause the flashing of the lamp and simultaneously cause a distinctive checking or proceed tone to be heard from the loudspeaker.

Since the checking signals are automatically cut out at the central station, as described, when speech is being transmitted, the checking signals will not interfere audibly with this speech. The locomotive engineer is provided, by the apparatus illustrated in Figures '1 and 8, with a transmitter for calling and speaking to the central station operator. The filaments of this transmitter are normally energized from the locomotive 32 volt supply. The plate circuits thereof are normally de-energized and the antenna 5| is normally uncoupled therefrom.

When the engineer desires to call the central station he may depress his transmitter switch 54 which, as illustrated in Figure 7, joins coil 21| of relay 212 between the direct current source available and ground. A resistor 213 reduces the flow of current in the relay winding to prevent damage to the relay coil 21 I.

In addition, the operation of switch 54, energizes the coil 214 of the antenna transfer and power transfer relays 55 and 64 respectively, and thus causes the consequent moving of the switch arms which in turn connects the antenna 5| to the .output of the transmitting circuits and applies the high potential available from the generator 206 to the transmitting anode circuits and disconnects this potential from the receiver circuits. i

The energization of relay coil 21| causes the movement of the switching members 212 downwardly as viewed in Figure '7 to close their respective circuits and as indicated, complete one circuit from the positive terminal of the direct current available at the terminals 264 through the switching member and through a variable resistor 216 to ground.

The variable tap of the resistor 216 then is joined in circuit through the primary of the transmitter input transformer I215, through the microphone 65 to ground. Thu's an energizing potential is impressed upon the microphone 65 which is preferably of the carbon type since relatively high gain is obtained immediately at the microphone. f

The other switching member of the relay 21 short circuits a section of a variable resistor 28|. This resistor is in series with a transmitting pilot light 66 and the series 'combination is joined to the terminals 204. The resistance in the trans- 2l mitting ypilot light circuit presented by resistor 28,! is normally suiificiently great to preclude the illumination of transmitting pilot bulb 56.

However, upon the operation of relay 212 and the short circuiting of a section of the resistor 28|,the lamp 6B glows to indicate that the transmitter is being energized. The transmitter may be of any conventional form and, as illustrated, essentially comprises an oscillator 282 having a tuned circuit 2.83 land a crystal284 for determinine the frequency thereof.

The `output of the oscillator is coupled to the control grid of la power amplifier 285, the plate circuit of which is energized from the high potential source `through inductance 286 and through radio frequency choke 281 and tank inductance L The screen-grid of the power amplier 285 is also energized from the high potential source through inductance 28B and through resistor 292.

ySou-nd wavesfwhen-impressed upon-the carbon -cuit thereof is `joined thereto through the in' ductance 285. The amplifiedsignals which appear in the output -circuit of the modulator 295 modulate the radio frequency carrier generated by the oscillator 282 -and its associated crystal .284.

Thus,when speech is impressed upon the microphone-65and theswitch 5 4-is closed, the antenna 5l will radiate a carriermodulated in accordance with the speech. fIf no speech is impressed upon the microphone, the vcarrier only will be radiated.

Theradiated signalswill be received at the receiver illustrated in Figure 4 at the central station and in the time intervening between two successive checking impulses, the radiated carrier or modulated carrier will cause the suppressor relay 4 8 of the central station to operate -to preclude thefurther transmission of checking V-or other signals'from-l the central station.

vThis traffic communication system may be employed wherever-mobile units are operated in a localized signaling area. Where .applied to rail- -road work and more speciiically -to classication :yards at freight -stations,the elementsof the apparatus may preferablyv be arranged as illustrated in Figures 5,..6,*9, 10,11, and 12.

"Thus, at the central lcontrol station, we may incorporate the loudspeaker, microphone and indicating lights into a single compact unit as illus- ,trated in-Figures and 6. The loudspeaker is mounted within a housing in a position slightly above ear-level 4wherevsounds may most .easily be detected. .A flexible or non-flexible arm -302 supports-the microphone Y26 within a'housing 303 attached to the ar-m at 304.

In addition, the housing also provides `supporting means for the three indicating lights at the central station4 schematically illustrated in Figure 1 and in the circuit diagrams of Figure 3. These lightsmaybe of va distinctive color and lare energized through the necessary wiring indicated in Figure 3, this wiring being carried through the, iieiiible arm. 302.

The entire .assembly of .microphona loudspeaker and 'checkinglights may be disposed zat 22 the central control point within ,the station which, in turn, may belocatedadjacent the-hump of the classication yard. t

If the operator is in an elevated position, with respect to the hump, .in a control tower, then the microphone and loudspeaker assembly indicated in Figures 5 and .6 may be disposed adjacent .a window overlooking the yard. -The foot switch 32 which, when depressed, permits the transmission of speech from the central station, may be disposed directly beneath the .combined microphone and loudspeaker assembly.

The central station operator `will always have the microphone available for speech transmission, and, by merely depressing the foot switch, may call a locomotive within the classification yard and relay the required instructions. Furthermore, vat all times the three indicating lights 4 1, t3, and 35 will be in his field of vision in order that he may ascertain the correct operation of the system.

Since the `operator will always be near the microphone and loudspeaker assembly, the calling of a locomotive engineer will immediately be apparent to the central station operator who will then acknowledge this c all and confer with the locomotive engineer.

As indicated in Figures 9, 10, and 11, the microphone of theI mobileunit may be of .similar construction. `Thus the microphone yd5 is supported upon a iiexible arm 3H which in turn is carried upon a support @i2 which may be securedto the roof of the locomotive, or other Vehicles, by a nlurality of screws 3,53.

The microphone -in thisqembodiment is mounted within a shockresistant housing in order that the vibration and the like experienced by the locomotive will not injure the sensitive microphone nor cause undue transmission of noise. Thus, as indicated in Figure 10,-themicrophone is supported substantially centrally within a housing 3 M which is joined to the lieXible arm 3i l atti-2.

The flexible arm carries the necessary microphone wires 315 therethrough to permit the energization thereof and the transmission of speech currents. The relatively large spa-ce between the microphone and the outer wall of the supporting housing lfitti-is packed with a highly-resilient material B16 or the like in order that the jarring of the housing will be eliectively damped and not be transmitted to the microphone itself.

The indicating lightsSS and 65 at the transmitter, which visually indicate the checking signal and show thelocomotive transmitter is no t in operation, may be mounted upon the microphone in order that the engineer, when speaking, may have a visual indication of the condition of the various system elements. The mounting of the microphone is most clearly illustrated in Figure 12, which is a pictorial illustration of the interior of a locomotive cab.

The engineer, as is well known, normally must .observe the roadway inperforming the various operations and cannot conveniently employhis hands to holdv the microphone. Thus, we prefer to suspend the microphone directly within the engineers field of vision by means of the flexible arm 3l I, by securing the support 312 to the roof of the cab, and extending the iiexible connector so that it projects inward with respect to the `window 32| of the locomotive.

The directional loudspeaker-51 employed within the locomotive cab may be disposed behindthe engineers seat 322 and directed towards him so that the speech signals will readily be audible.

23 Accordingly, the engineer will receive transmitted speech signals by loudspeaker l and will at all times have the checking signal in his leld of Vision to ascertain the proper working order of the complete communication system.

Ihe transmitting switch 54 may be disposed adjacent the sash of the window 32| in order that the engineer may conveniently operate this switch without moving from his normal position. Since the microphone, as was previously mentioned, is directly within his eld of vision, he will at all times be able to observe operation of the checking or proceed signal and transmitting pilot light indicators.

It will now be obvious that various modifications of this speciiic disclosure will be evident to th-ose skilled in the art. Accordingly, I prefer not to be bound by the specific disclosure above, but by the appended claims.

I claim:

1. In a signaling system, a central station including a receiver, means for impressing received signals on said receiver, a radiator, means for impressing a generated signal upon said radiator, means for sequentially and periodically operating said second impressing means, and automatic means at said central station responsive to signal energy from a remote point to prevent said periodic impression of said generated signal upon said radiator during reception of said signal energy from said remote point.

2. In a signaling system for establishing a twoway radio aural communications and automatic supervisory signaling between a control station and a-remote mobile unit, a carrier wave transmitter for said control station, manually-operable switching means for connecting circuits of said transmitter to effect speech modulation of carrier wave energy emitted by said transmitter, a source of control signal energy, automatic means for periodically controlling emission of a carrier wave by said transmitter and concurrently impressing said control signal energy Ion said carrier Wave, receiving means for said mobile unit responsive to modulated carrier Wave energy from said transmitter, said receiving means including a sound reproducing device, transmitting means for said mobile unit for emitting carrier wave energy from said mobile unit, receiving means for said control station responsive to signal energy from said mobile unit, and aut-omomatic means located with said control station receiving means including a relay operable by a received signal from said mobile unit, said relay being effective in preventing operation of said rst mentioned automatic means for periodically controlling emission of said carrier wave from said control station during reception of signal energy from said mobile unit.

3. In a traflic signaling system for establishing communications and automatic supervisory signaling between a control station and a remote station, a carrier Wave transmitter for said control station, manually-operable switching means for connecting circuits of said transmitter to effect speech modulation of carrier wave energy emitted by said transmitter, a source of control signal energy, automatic means for periodically controlling emission of a carrier wave by said transmitter and concurrently impressing said control signal energy on said carrier wave, receiving means for said central station responsive to carrier wave energy from said remote station, and relay control means connected with said receiving means, said relay being responsive to signal 24 energy from said remote station and operable to prevent periodic emission of carrier Wave energy by said control station during reception of signal energy from said remote station.

4. In a traiiic signaling system for effecting automatic supervisory signaling between a central control station and a remote mobile unit, 'a carrier wave transmitter for said trafc control station, a second carrier wave transmitter for'l said remote mobile unit, carrier wave receiving means individual to said trac control station and responsive to carrier wave energy from said mobile unit, carrier wave receiving means individual to said mobile unit and responsive to carrier wave energy from said central station, a source oi audio frequency control signal energy, automatic switching means for periodically effecting emission of a carrier wave by said central station transmitter and simultaneously impressing said control signal energy on said carrier Wave, and a lockout relay connected to the carrier wave receiving means of said central station, said relay being responsive to received carrier Wave energy from the transmitter of said mobile unit, said relay having switching means operable to prevent periodic transmission of carrier wave energyby the central station during reception of carrier wave energy from Said mobile unit.

5. In a traic signaling system for eiecting automatic supervisory signaling between a traic control station and a remote mobile unit, a carrier wave transmitter for said traflic control station, a second carrier wave transmitter for said remote mobile unit, carrier wave receiving means individual to said trafc control station and responsive to carrier Wave energy from said mobile unit, carrier wave receiving means individual to said mobile unit and responsive to carrier wave energy from said control station, a source of audio frequency control signal energy, automatic switching means for periodically effecting emission of a carrier wave by said control station transmitter and concurrently impressing said control signal energy on said carrier wave, a visual indicator disposed at said control station, and a lockout relay connected to the carrier wave receiving means of said control station, and responsive to received carrier wave energy from the transmitter of said mobile unit, said relay having switching means operable to prevent periodic transmission of carrier wave energy by the control station during reception of carrier wave energy from said mobile unit, said relay also having a second switching means operable to actuate said visual indicator during reception of a carrier wave from said mobile unit.

6. In a traffic signaling system for establishing two-way aural communications and automatic supervisory signaling between a traffic control station and a remote mobile unit, a carrier Wave transmitter for said traic control stati-on, a second carrier wave transmitter for said remote mobile unit, carrier wave receiving mean-s individual to said traiiic control station and normally responsive to carrier wave energy from said mobile unit, carrier wave receiving means individual to said mobile unit and normally responsive to carrier wave energy from said control station, a source of audio frequency control signal energy, automatic switching means for periodically effecting emission of a carrier wave by said control station transmitter and concurrently impressing said control signal energy on said carrier wave, manually operable switching means for connecting circuits of said transmitter to effect 

